1. Field
This invention pertains to the field of vision diagnostics, and in particular to a method and apparatus for characterizing conical shape and/or structure.
2. Description
There are a number of situations where it is desirable or necessary to determine the thickness of the cornea of an eye, or the shape of its back surface. For example, in the case that a LASIK procedure is being considered, determination of corneal thickness may be used to aid treatment planning.
There are a few non-contact methods of measuring corneal thickness. These include optical coherence topography and Scheimpflug photography.
However, it would be desirable to provide alternative systems that can characterize a back surface of a corneal and/or measure corneal thickness. It would also be desirable to provide a method of characterizing a back surface of a cornea and/or measure corneal thickness.
In one aspect of the invention, a system comprises: a light pattern generator comprising a plurality of light spots configured to illuminate a front surface and a back surface of a cornea of an eye with polarized light; one or more detectors positioned to receive one or more of a first plurality of spot images from light reflected off the front surface of the cornea, and a second plurality of spot images from light reflected off the back surface of the cornea, the light reflected off the front surface of the cornea having a first polarization and the light reflected off the back surface of the cornea having a second polarization different from the first polarization; a polarization element disposed in an optical path between the back surface of the cornea of the eye and the one or more detectors, the polarization element being configured to attenuate an intensity of the light reflected off the front surface of the cornea by an amount greater than an amount by which it attenuates the light reflected off the back surface of the cornea; and a processor configured to determine a geometric characteristic of the cornea of the eye using at least the second plurality of spot images received by the one or more detectors.
In another aspect of the invention, a method comprises: illuminating a front surface and a back surface of a cornea of an eye with polarized light from a light pattern generator comprising a plurality of light spots; directing light reflected off the front surface of the cornea and light reflected off the back surface of the cornea to a polarization element, the polarization element being configured to attenuate an intensity of the light reflected off the front surface of the cornea by an amount greater than an amount by which it attenuates the light reflected off the back surface of the cornea; receiving at one or more detectors one or more of a first plurality of spot images from light reflected off the front surface of the cornea, and a second plurality of spot images from light reflected off the back surface of the cornea, the light reflected off the front surface of the cornea having a first polarization and the light reflected off the back surface of the cornea having a second polarization different from the first polarization; and determining a geometric characteristic of the cornea of the eye using at least the second plurality of spot images received by the one or more detectors.